36 FLIGHT International, 2 January 1964
Missiles and Spaceflight
ALTITUDE
MILES
ASPECTS OF THE
AEROSPACE PLANE 5,000
Fig I Aerospace vehicle performance
10,000 15,000
SPEED FT/SEC
20,000
This article is based on extracts from "Some Fundamental Aspects
of the Aerospace Plane Concept," presented at the recent British
Interplanetary Society symposium on aerospace vehicles by C. R.
Turner of Hawker Siddeley Aviation Ltd. Other papers from the
symposium were abstracted in our issues of December 19 and
December 26, 1963.
THE major mission envisaged for the aerospace plane is that offerrying supplies and personnel between the Earth and satellitesin near-Earth orbit. For this type of mission an operating
height above the Earth's surface of the order of about 200 miles
should suffice. This ferrying operation might be used for the
assembly of interplanetary missions, or alternatively off-loading
them on return to near-Earth orbit, and also for setting up scientific
space laboratories. All this implies provision for rendezvous and
docking, and to this end the capability of the vehicle for pre-orbital
manoeuvre might be an important design factor when assessing the
comparative features of a rocket first stage or an airbreathing first
stage.
Other foreseeable missions include the conducting of scientific
experiments and the inspection and possible servicing of communi-
cation, navigation and meteorological satellites. For some of these
missions the operating heights would have to be greater than 200
miles, unless considerable orbiting manoeuvre is built into these
satellites for such a purpose, involving a payload penalty, more
severe guidance and control requirements and would in fact imply
a more advanced concept. Also, in general, any manned mission
where information is required with the minimum of delay might
justify an aerospace plane concept. With the assumption that the
concept will enable launching from more conventional sites,
possibly in Europe, the capability of launch into an orbit other than
through its point of launch is a very important aspect of an aero-
space plane operation. Could it be used, for instance, to undertake
those missions for which an equatorial launching site is considered
necessary?
It must be realized that this range of missions with corresponding
payloads cannot be accomplished economically with a single design.
One does not expect one type of civil airliner to be suitable for all
operating conditions. These designs will certainly differ radically
one from the other. For example, the propulsion combination
required for a low-payload mission may differ considerably from
that requiring a high payload.
Ultimately, and this will be a difficult decision, a choice will have
to be made, for the first generation aerospace plane at least, regard-
ing the particular missions and payload range on which it is best to
concentrate. It has been suggested that the payload might be in the
region of about five tons so as to compete neither with payloads
associated with large US rockets, nor with the large US spaceplane
concepts.
Regarding most of these missions, the inclusion of a man in the
system seems imperative, in particular for the requirements of
rendezvous, docking and landing at a specified site. It is realized
that the inclusion of a man in a space system requires additional
equipment to provide life support and more duplication than for
an unmanned mission. Obviously the man must not be taken along
just for the ride, but must be justified as an essential part of the
system.
Basic Design Considerations Bearing in mind
these missions, let us attempt to define the principal characteristics
of an aerospace plane. These must be such as to show positive
advantages over any existing conventional systems or developments
thereof. As it is inconceivable that, on this side of the Atlantic,
any project based on this concept will be completed in under ten
years, the problem of creating a system that will not be superseded
before it is operational is very important.
To my mind the basic characteristics of an aerospace plane should
be the following:—
(a) The vehicle's stages should be recoverable whether rocket or
airbreathing.
(a) The final stage should be capable of entering an orbit of at
least 200 miles in the first instance; this may be extended in the
light of experience and requirements.
(c) It should be capable of considerable sub-orbital manoeuvre.
To attain orbital planes that periodically pass through the launching
point, manoeuvrability that would effectively reduce the time delay
should be a capability. Regarding orbital planes inclined to the
equatorial plane at an angle less than the launching latitude,
manoeuvring capability to enter these orbital planes should exist,
although this will depend on the latitude of the launching site.
(d) It should be capable of a limited manoeuvring capability in
orbit. It must be realized that manoeuvring operations such as
orbit changing, repositioning in orbit, etc, involve a very large
weight penalty. It can be calculated, based on a 5,0001b payload,
that even a 1° orbit change can involve a weight penalty of about
3501b, a 30° orbit change about 5,0001b. To "catch up" a 30° lag
in a 200-mile circular orbit by direct orbit transfer requires again
about 8501b. However, these figures do imply a reasonably quick
manoeuvre time, for the weight penalties can often be considerably
reduced if a longer time is acceptable. The point, however, is that
within the present capabilities the idea that the spaceplane in orbit
can enjoy the manoeuvring capabilities of a fighter should be
dispelled. Finally, the vehicle should be able to rendezvous and
dock as required by the missions.
(e) Re-entry should be possible whenever required and the vehicle
should have the aerodynamic capability (moderately high hyper-
sonic L/D) and good subsonic characteristics to enable it to glide
and land, with power when required, to a pre-determined site. The
main problems encountered here are high deceleration, heating
rates, total heat input, and acceptable landing speeds, etc.
(/) The vehicle, in its final form at least, should be manned; this
will undoubtedly suggest a minimum orbital weight of at least
4,0001b.
(g) To enable reasonably fit, but not specifically trained, personnel
to engage in these missions the maximum vehicle acceleration and
deceleration should be restricted to a value between 1.5g and 2g,
although this will depend on the rate of change of acceleration, and
its duration.
These requirements represent to my mind the desirable features
of an aerospace plane and those which taken as a whole should lead